1. Field of the Invention
The present invention relates to an optical pickup device used in an optical disc driving apparatus for recoding and reproducing data with respect to an optical disc, and especially relates to a defocus adjustor used for adjusting a position of a photo-sensor against an optical system in the optical pickup device.
2. Description of the Related Art
Many technologies are conventionally proposed for easing assembly and adjustment of an optical pickup device. In a conventional optical pickup device, for example, shown in publication gazette of Japanese patent application 9-198689, a flexible printed circuit board is used for connecting between a photo-sensor for sensing reflected laser beam from an optical disc and a controller for controlling the optical pickup device. The flexible printed circuit board is biased toward a holder of the optical pickup device by a plate spring.
In another conventional optical pickup device, for example, shown in publication gazette of Japanese patent application 2000-293879, a coupling hook for hooking a printed circuit board on which a photo-sensor is mounted is provided on a holder of the optical pickup device, so that the printed circuit board can easily be fixed on the holder.
In the optical pickup device, it is preferable that a photo-sensing surface of the photo-sensor is disposed corresponding to a focused position of the reflected laser beam and perpendicular to an optical axis of the reflected laser beam so as to increase the sensitivity of the photo-sensor. Thus, there is an optical pickup device having a defocus adjustor by which a position and an inclination of a photo-sensor can be adjusted precisely while an optical disc driving apparatus is assembled. A conventional optical pickup device, for example, shown in publication gazette of Japanese patent application 7-235059, comprises a fixing member having a U-shaped section for biasing a printed circuit board on which a photo-sensor is mounted toward an optical axis of a reflected laser beam, and an adjusting screw which is engaged with an end of the printed circuit board and is tightened on a holder. Defocus of the photo-sensor with respect to an optical system can be adjusted with using a spring effect of the fixing member due to tightening and loosening the adjusting screw.
Applicant has proposed an optical pickup device having a defocus adjustor (which is not known by publication). The optical pickup device with the defocus adjustor proposed by the applicant is described with reference to FIGS. 5, 6A, 6B, 7A and 7B.
The optical pickup device 100 comprises a laser diode 44 for emitting a laser beam L, a half mirror 45 for reflecting the laser beam L emitted from the laser diode 44 to an optical disc D and through which a reflected laser beam L′ reflected by the optical disc D passes, a collimator lens 46a for expanding a diameter of the laser beam L and for converting the laser beam L to a parallel beam, a focusing lens 46b for focusing the laser beam L on a data recording face of the optical disc D, and a photo-sensor 47 for sensing the reflected laser beam L′ reflected by the data recording face of the optical disc D.
FIGS. 7A and 7B show a configuration of the defocus adjustor and a method for adjusting the defocus. As can be seen from FIGS. 7A and 7B, the photo-sensor 47 is mounted on a flexible printed circuit board 48, and terminals 47a of the photo-sensor 47 are connected to circuit patterns on the flexible printed circuit board 48. The flexible printed circuit board 48 is bonded on a plate spring 101. A first end 101a of the plate spring 101 is fixed on a fixing face 102a of a holder 102 by screws 52, and a second end 101b of the plate spring 101 is adjustably fixed on the holder 102 by an adjusting screw 51.
The fixing face 102a of the holder 102 is formed on a plane substantially perpendicular to an optical axis of the reflected laser beam L′. The plate spring 101 is formed, for example, by punching and pressing a metal plate so as to have a bending portion 101c disposed between the end 101a and the position of the photo-sensor 47. When the first end 101a of the plate spring 101 is fixed on the fixing face 102a of the holder 102 by the screws 52 as shown in FIG. 7A, the position of the photo-sensor 47 of the plate spring 101 takes a state having a predetermined angle against the optical axis of the reflected laser beam L′. Subsequently, when the adjusting screw 51 is engaged with the second end 101b of the plate spring 101 and fixed on the holder 102 as shown in FIG. 7B, the plate spring 101 is warped to be straight, so that a photo-sensing surface 47b of the photo-sensor 47 becomes substantially perpendicular to the optical axis of the reflected laser beam L′, which is suitable posture for sensing the reflected laser beam L′.
At this time, the plate spring 101 generates a stress against the tightening of the adjusting screw 51, which causes a spring effect suitable for adjusting the defocus of the photo-sensor 47 with respect to the optical system. Thus, when the adjusting screw 51 is excessively tightened, the position and inclination of the photo-sensing surface 47b of the photo-sensor 47 can be restored by loosening the adjusting screw 51 so that the defocus of the photo-sensor 47 can be fine adjusted.
The above-mentioned conventional optical pickup devices shown in the publication gazettes 9-198689 and 2000-293879, however, have no defocus adjustor, so that it is difficult to adjust the defocus of the photo-sensor. In the conventional optical pickup device shown in the publication gazette 7-235059, the bending angle of the U-shaped section of the fixing member can easily be varied in the manufacturing thereof. When the bending angle of the U-shaped section of the fixing member is varied, the spring effect of the fixing member becomes unstable, so that it is troublesome to adjust the defocus of the photo-sensor. Thus, the conventional optical pickup device is not suitable for mass production.
The optical pickup device proposed by the applicant and shown in FIGS. 5, 6A, 6B, 7A and 7B has a disadvantage that the bending angle of the plate spring 101 is easily be varied in the manufacturing thereof. When the bending angle of the plate spring 101 is varied, the spring effect due to the stress generated by the plate spring 101 against the tightening of the adjusting screw 51 becomes unstable. Thus, it becomes troublesome to adjust the defocus of the photo-sensor 47, so that the optical pickup device 100 proposed by the applicant is not suitable so much for mass production. Furthermore, it is impossible to bond the flexible printed circuit board 48 on the plate spring 101 by thermo compression with using a thermo compression roller, since the plate spring 101 has a bending portion 101c. Thus, the bond strength between the plate spring 101 and the flexible printed circuit board 48 becomes uneven.